1. Field of the Invention
This invention relates to the upgrading of liquids containing aromatics and more particularly to the catalytic treatment of highly aromatic petroleum and coal derived liquids to effect removal of sulfur, nitrogen and oxygen and to reduce Conradson Carbon Residue (CCR).
2. Description of the Prior Art
The use of hydrotreating (HDT) to upgrade residue hydrocarbon fractions for use as charge stocks for catalytic cracking was well known in the art by the 1960's. Hydrotreating, as used herein, is meant to encompass those processes using hydrogen in the presence of catalysts in order to remove undesirable compounds from hydrocarbons, i.e. to upgrade said hydrocarbons.
By 1960, it was recognized that hydrotreatment of residues could be used for demetalation, desulfurization, CCR reduction and denitrogenation. There was universal recognition at that time in the art that hydrogenation catalysts comprising Group VI (Cr, Mo, W) and Group VIII metals or their oxides or sulfides deposited on porous refractory supports were extremely useful in hydrotreating processes. Preferred catalysts for hydrotreating were considered to be cobalt-molybdate or nickel-cobalt-molybdate supported on alumina. These catalysts are generally referred to as "conventional HDT catalysts."
The pore size distribution of the HDT catalyst is a very important parameter in determination of the activity of the catalyst. Large pore catalysts generally possess greater demetalating activity and smaller pore catalysts generally posses lower demetalating activity, but higher desulfurizing activity. U.S. Pat. No. 3,730,879 teaches an HDT process comprising a multi-layered arrangement of catalyst with different pore distributions. In the first bed there is used a smaller pore catalyst which is more selective for desulfurization; and in the second downstream bed there is used a larger pore catalyst which is more selective for removal of metal contaminants. According to U.S. Pat. No. 3,730,879, the desulfurization catalyst of the first bed has a catalyst characterized by a pore diameter distribution as follows: &lt;25% 0-100 A; &gt;50% 100-200 A; and the remainder 200-600 A. The demetalation catalyst of the second bed has a catalyst characterized by a pore diameter distribution as follows: &lt;20% 0-100 A; &lt;45% 100-200 A; and balance 200-600 A.
The average pore diameter size for HDT catalysts in desulfurization processes is usually 100-200 A. Such average pore diameter size is disclosed in U.S. Pat. Nos. 3,393,148; 3,674,680; 3,764,565; 3,841,995 and 3,882,049.
Processes for the demetalation and desulfurization of residual oil fractions using conventional HDT catalysts with at least 60% of its pore volume in pores of 100 A to 200 A diameter and at least 5% of its pore volume in pores having diameters greater than 500 A are disclosed in U.S. Pat. Nos. 3,876,523 and 4,016,067.
U.S. Pat. No. 3,902,991 discloses a hydrodesulfurization process for residual oil fractions which uses a conventional HDT catalyst characterized by having at least 50% of its total pore volume in pores having a diameter size range of 65 to 150 A. Another hydrodesulfurization process for resids is described in U.S. Pat. No. 3,730,879, wherein one of the catalysts is characterized by having at least 50% of its total pore volume in pores having radii in the size range of 50-100 A. Still another resid hydrodesulfurization process is disclosed in U.S. Pat. No. 3,814,683. In this patent, the conventional HDT catalyst is characterized by having at least 65% of its total pore volume in pores having a diameter size of 80-180 A.
Other hydrodesulfurization processes using a conventional HDT catalyst characterized by a specific pore size distribution are disclosed in U.S. Pat. Nos. 4,032,435; 4,051,021; 4,069,139 and 4,073,718.
Whereas a great amount of attention has been given to hydrotreating petroleum residual fractions, much less emphasis has been placed specifically on highly aromatic petroleum and coal derived liquids. U.S. Pat. No. 3,812,028 describes a process for hydrotreating fossil fuels containing polynuclear aromatics utilizing a catalyst comprising activated carbon and a metallic component. In U.S. Pat. No. 4,051,021, a hydrodesulfurization process using a catalyst with a specified pore size distribution is disclosed. In such hydrodesulfurization process, a hydrocarbon feed is contacted with a conventional HDT catalyst having greater than 50 percent of its total pore volume of absolute diameter ranging from about 70 Angstroms to about 100 Angstroms.
With the ever increasing demands on fossil fuels as a source of energy and the ever decreasing supplies of crude petroleum within the United States the nation must place more emphasis on the use of coal. Yet the people of this country have mandated through their representatives that they do not want the anticipated increased use of coal to degrade their environment. Thus the liquid products derived from such sources as coal, shale oil and tar sands must be upgraded in order to remove possible pollutants before utilization of such liquids.